Once you see that an answer is not serving its question properly anymore, it should be tossed away. It's just their natural life cycle.
They usually kick and scream, raising one hell of a ruckus when we ask them to leave. Especially when they have been with us for a long time.
You see, too many actions have been based on those answers. Too much work and energy invested on them. They feel so important, so full of themselves. They will answer to no one. Not even to their initial question!
The hardest thing about customer interviews is knowing where to dig. An effective interview is more like a friendly interrogation. We don’t want to learn what customers think about the product, or what they like or dislike — we want to know what happened and how they chose... To get those answers we can’t just ask surface questions, we have to keep digging back behind the answers to find out what really happened.
The man of today planes to perfection a board with a planing machine in a few seconds. The man of yesterday planed a board reasonably well with a plane. Very primitive man squared a board very badly with a flint or a knife. Very primitive man employed a unit of measurement and regulating lines in order to make his task easier. The Greek, the Egyptian, Michaelangelo or Blondel employed regulating lines in order to correct their work and for the satisfaction of their artist’s sense and of their mathematical thought. The man of today employs nothing at all and the result is the boulevard Raspail.